At least 19 people were killed Saturday in multiple airstrikes led by a Saudi coalition in the port city of Hodeida, Yemen, Houthi rebels said.

Youssef al-Hadiri, a spokesman for the rebel-controlled Health Ministry, said coalition warplanes hit two buses carrying civilians in Hodeida's Jabal Ras area, killing at least 19 people and injuring 30 others.

The dead included women and children, according to the official.

"The final toll is not determined yet because body parts of many victims are mixed with each other," al-Hadiri told German Press Agency (DPA).

Earlier Saturday, he said at least 17 civilians were killed and more than 20 others injured in the attack.

Witnesses told dpa that all the people inside the bombarded buses were civilians, who were trying to flee fighting in their area between the rebels and government forces.

So far, there has been no comment from the Saudi-led alliance, which has been fighting Yemen's Iran-linked rebel Houthis since 2015.

Rebel-controlled Hodeida has been the target of a coalition-backed offensive since June.

The government forces have since seized Hodeida's airport, and are pushing to retake the city and its port, through which an estimated 80 per cent of imports and aid reach Yemen.

Aid agencies have repeatedly warned that the offensive would have devastating consequences for the country's population, which is already on the brink of famine.

The United Nations has labeled Yemen the world's worst humanitarian crisis. After three and a half years of war, 22 million Yemenis — or three-quarters of the population — depend on aid supplies.

One of the Arab world's poorest countries, Yemen has been embroiled in a devastating power struggle between the Saudi-backed government and the Houthis since late 2014.

The conflict intensified when Saudi Arabia and other allies started an air campaign in March 2015 to halt the Iran-backed group's advance towards Aden, the temporary seat of the government.